Two protons (each with a rest mass of 1.67x10^(-27) kg) are initially moving with equal speeds in opposite directions. The two protons continue to exist after the collision between them that also produces a new particle that I will call "particle X". The rest mass of particle X is 9.75x10^(-28) kg.
Note:
1M = 10^6 (1 Mega)
c = 3.00x10^8 m/s
1 eV = 1.60x10^(-19)